1. Field of the Invention
The present invention relates to a semiconductor device having a metal-oxide-semiconductor field effect transistor (MOSFET), a capacitor, and a resistor, all on the same substrate, and also relates to a method of manufacturing the semiconductor device.
2. Description of the Related Art
In recent years, capacitors and resistors have been widely used in analog circuits. Further, along with increase in circuit scale and degree of integration, a semiconductor device in which a transistor element, a capacitor, and a resistor are mounted together on the same semiconductor substrate has become the mainstream.
In particular, in the analog circuits, resistors of high resistance made of polysilicon are widely used. In this case, as a useful method for stably increasing the resistance of the resistor, there is employed a method of reducing the thickness of the resistor. Meanwhile, since a manufacturing process is simplified in an effort to unify the structure and share the process in a method of manufacturing the respective circuit element, in many cases, a gate electrode of the transistor and a lower electrode of the capacitor; and an upper electrode of the capacitor and the resistor are respectively made of the same polysilicon film at the same time.
Accordingly, reduction of the thickness of the resistor in order to increase the resistance of the resistor simultaneously reduces the thickness of the upper electrode of the capacitor.
Reduction of the thickness of the upper electrode of the capacitor may cause the following troubles.
(a) A contact hole at the upper electrode of the capacitor is shallow, and hence the upper electrode is easily subjected to over etching. The reliability deteriorates and passing through of a contact causes failure of the capacitor.
(b) Thin thickness of the upper electrode causes the resistance to be high, making voltage dependence of a parasitic resistance or the like large, which causes reduction in function as an electrode.
Japanese Published Patent Application No. 2003-282726 discloses a method of manufacturing a semiconductor device including contacts formed in contact holes having different lengths, in which a surface of the circuit element corresponding to the short contact hole is prevented from being subjected to over etching. According to Japanese Published Patent Application No. 2003-282726, a nitride film is formed on each circuit element as a stopper film, to thereby prevent the circuit element from being subjected to over etching when etching for forming the contact hole is performed.
However, when the high resistance resistor necessary for the analog device and the capacitor are formed of the same polysilicon film, the method of manufacturing a semiconductor device described in Japanese Published Patent Application No. 2003-282726 can solve the above-mentioned trouble (a), but cannot solve the above-mentioned trouble (b), and hence a capacitor with a sufficient function cannot be manufactured.